Metalhead is a mechanical turtle created by Donatello's quirky scientist ally, Harold Lilja. After being kidnapped by Baxter Stockman and forced to use his intellect for nefarious means, Lilja decided he needed to work on keeping himself secure. Having seen Donatello in action, he designed his security robot after him, believing his Mutant Turtle body was, at least in part, a factor in his abilities. Angel uncovered the robot Turtle in Lilja's lab and called it Metalhead.
While Lilja was demonstrating the robot's abilities, its circuits fried. He had programmed StockGen Enterprises' entire employee database into its memory as targets, which unfortunately included April. After Donatello had failed to defeat the rogue robot, Angel donned Lilja's exo-suit that he had shown them before, and taken Metalhead out of commission.
Donatello later used Metalhead as his avatar when communicating with Shredder, so that he wouldn't have to risk himself physically by going to the Foot Clan's domain. The use of Metalhead later became more necessary when Donatello was mortally injured by Rocksteady and Bebop, and it became necessary for Lilja and Professor Honeycutt to transfer Donatello's mind into the robot body.
The Metalhead body was destroyed in an explosion when Donatello's mind was transferred back to his flesh-and-blood body. Some time later, he attempted to repair Metalhead, only to discover that the robot had retained a digital copy of his mind, which Michelangelo dubbed Metal-Don. However, the robotic nature of Metalhead began to eat away at Metal-Don's mind, driving him to violent and erratic actions. The Metalhead body was discarded in favor of a newer version that Lilja had constructed.
When last seen, the empty Metalhead body was left in Donatello's laboratory.
